A rice small GTPase, Rab6a, is involved in the regulation of grain yield and iron nutrition in response to CO2 enrichment

Glucose-G protein signaling plays a crucial role in tomato resilience to high temperature and elevated CO2

Global climate change is accompanied by carbon dioxide (CO2) enrichment and high temperature (HT) stress; however, how plants adapt to the combined environments and the underlying mechanisms remain largely unclear. In this study, we show that elevated CO2 alleviated plant sensitivity to HT stress, with significantly increased apoplastic glucose (Glc) levels in tomato (Solanum lycopersicum) leaves. Exogenous Glc treatment enhanced tomato resilience to HT stress under ambient CO2 conditions. Cell-based biolayer interferometry, subcellular localization, and Split-luciferase assays revealed that Glc bound to the tomato regulator of G protein signaling 1 (RGS1) and induced RGS1 endocytosis and thereby RGS1-G protein α subunit (GPA1) dissociation in a concentration-dependent manner. Using rgs1 and gpa1 mutants, we found that RGS1 negatively regulated thermotolerance and was required for elevated CO2-Glc-induced thermotolerance. GPA1 positively regulated the elevated CO2-Glc-induced thermotolerance. A combined transcriptome and chlorophyll fluorescence parameter analysis further revealed that GPA1 integrated photosynthesis- and photoprotection-related mechanisms to regulate thermotolerance. These results demonstrate that Glc-RGS1-GPA1 signaling plays a crucial role in the elevated CO2-induced thermotolerance in tomato. This information enhances our understanding of the Glc-G protein signaling function in stress resilience in response to global climate change and will be helpful for genetic engineering approaches to improve plant resilience.

Natural genetic variation underlying the negative effect of elevated CO2 on ionome composition in Arabidopsis thaliana

The elevation of atmospheric CO2 leads to a decline in plant mineral content, which might pose a significant threat to food security in coming decades. Although few genes have been identified for the negative effect of elevated CO2 on plant mineral composition, several studies suggest the existence of genetic factors. Here, we performed a large-scale study to explore genetic diversity of plant ionome responses to elevated CO2, using six hundred Arabidopsis thaliana accessions, representing geographical distributions ranging from worldwide to regional and local environments. We show that growth under elevated CO2 leads to a global decrease of ionome content, whatever the geographic distribution of the population. We observed a high range of genetic diversity, ranging from the most negative effect to resilience or even to a benefit in response to elevated CO2. Using genome-wide association mapping, we identified a large set of genes associated with this response, and we demonstrated that the function of one of these genes is involved in the negative effect of elevated CO2 on plant mineral composition. This resource will contribute to understand the mechanisms underlying the effect of elevated CO2 on plant mineral nutrition, and could help towards the development of crops adapted to a high-CO2 world.

A gene regulatory network in Arabidopsis roots reveals features and regulators of the plant response to elevated CO2

The elevation of CO₂ in the atmosphere increases plant biomass but decreases their mineral content. The genetic and molecular bases of these effects remain mostly unknown, in particular in the root system, which is responsible for plant nutrient uptake. To gain knowledge about the effect of elevated CO₂ on plant growth and physiology, and to identify its regulatory in the roots, we analyzed genome expression in Arabidopsis roots through a combinatorial design with contrasted levels of CO₂ , nitrate, and iron. We demonstrated that elevated CO₂ has a modest effect on root genome expression under nutrient sufficiency, but by contrast leads to massive expression changes under nitrate or iron deficiencies. We demonstrated that elevated CO₂ negatively targets nitrate and iron starvation modules at the transcriptional level, associated with a reduction in high-affinity nitrate uptake. Finally, we inferred a gene regulatory network governing the root response to elevated CO₂ . This network allowed us to identify candidate transcription factors including MYB15, WOX11, and EDF3 which we experimentally validated for their role in the stimulation of growth by elevated CO₂ . Our approach identified key features and regulators of the plant response to elevated CO₂ , with the objective of developing crops resilient to climate change.

The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal

The elevation of atmospheric CO₂ concentration has a strong impact on the physiology of C3 plants, far beyond photosynthesis and C metabolism. In particular, it reduces the concentrations of most mineral nutrients in plant tissues, posing major threats on crop quality, nutrient cycles, and carbon sinks in terrestrial agro-ecosystems. The causes of the detrimental effect of high CO₂ levels on plant mineral status are not understood. We provide an update on the main hypotheses and review the increasing evidence that, for nitrogen, this detrimental effect is associated with direct inhibition of key mechanisms of nitrogen uptake and assimilation. We also mention promising strategies for identifying genotypes that will maintain robust nutrient status in a future high-CO₂ world.

A tale of two metals: Biofortification of rice grains with iron and zinc

Iron (Fe) and zinc (Zn) are essential micronutrients needed by virtually all living organisms, including plants and humans, for proper growth and development. Due to its capacity to easily exchange electrons, Fe is important for electron transport in mitochondria and chloroplasts. Fe is also necessary for chlorophyll synthesis. Zn is a cofactor for several proteins, including Zn-finger transcription factors and redox metabolism enzymes such as copper/Zn superoxide dismutases. In humans, Fe participates in oxygen transport, electron transport, and cell division whereas Zn is involved in nucleic acid metabolism, apoptosis, immunity, and reproduction. Rice (Oryza sativa L.) is one of the major staple food crops, feeding over half of the world's population. However, Fe and Zn concentrations are low in rice grains, especially in the endosperm, which is consumed as white rice. Populations relying heavily on rice and other cereals are prone to Fe and Zn deficiency. One of the most cost-effective solutions to this problem is biofortification, which increases the nutritional value of crops, mainly in their edible organs, without yield reductions. In recent years, several approaches were applied to enhance the accumulation of Fe and Zn in rice seeds, especially in the endosperm. Here, we summarize these attempts involving transgenics and mutant lines, which resulted in Fe and/or Zn biofortification in rice grains. We review rice plant manipulations using ferritin genes, metal transporters, changes in the nicotianamine/phytosiderophore pathway (including biosynthetic genes and transporters), regulators of Fe deficiency responses, and other mutants/overexpressing lines used in gene characterization that resulted in Fe/Zn concentration changes in seeds. This review also discusses research gaps and proposes possible future directions that could be important to increase the concentration and bioavailability of Fe and Zn in rice seeds without the accumulation of deleterious elements. We also emphasize the need for a better understanding of metal homeostasis in rice, the importance of evaluating yield components of plants containing transgenes/mutations under field conditions, and the potential of identifying genes that can be manipulated by gene editing and other nontransgenic approaches.

Mining of Potential Gene Resources for Breeding Nutritionally Improved Maize

Maize is one of the leading food crops and its kernel is rich in starch, lipids, protein and other energy substances. In addition, maize kernels also contain many trace elements that are potentially beneficial to human health, such as vitamins, minerals and other secondary metabolites. However, gene resources that could be applied for nutrient improvement are limited in maize. In this review, we summarized 107 genes that are associated with nutrient content from different plant species and identified 246 orthologs from the maize genome. In addition, we constructed physical maps and performed a detailed expression pattern analysis for the 246 maize potential gene resources. Combining expression profiles and their potential roles in maize nutrient improvement, genetic engineering by editing or ectopic expression of these genes in maize are expected to improve resistant starch, oil, essential amino acids, vitamins, iron, zinc and anthocyanin levels of maize grains. Thus, this review provides valuable gene resources for maize nutrient improvement.

The small GTPase NtRHO1 negatively regulates tobacco defense response to tobacco mosaic virus by interacting with NtWRKY50

Small GTPases play critical roles in the regulation of plant growth and development. However, the mechanism of action of small GTPases in plant response to virus infection remains largely unknown. Here, the gene encoding a Rho-type GTPase, NtRHO1, was identified as one of the genes up-regulated after tobacco mosaic virus (TMV) infection. Subcellular localization of NtRHO1 showed that it was located in the cytoplasm, plasma membrane, and nucleus. Transient overexpression of NtRHO1 in Nicotiana benthamiana accelerated TMV reproduction and led to the production of reactive oxygen species. By contrast, silencing of NtRHO1 reduced the sensitivity of N. benthamiana to TMV-GFP. Further exploration revealed a direct interaction between NtRHO1 and NtWRKY50, a positive regulator of the N. benthamiana response to virus infection. Yeast one-hybrid and electrophoretic mobility shift assays showed that this regulation was related to the capacity of NtWRKY50 to bind to the WK-box of the PR1 promoter, which was weakened by the interaction between NtRHO1 and NtWRKY50. Thus, our results indicate that the small GTPase NtRHO1 plays a negative role in tobacco response to TMV infection by interacting with transcription factor NtWRKY50, resulting in reduced plant immunity.

OsGF14b is involved in regulating coarse root and fine root biomass partitioning in response to elevated [CO2] in rice

Elevated [CO₂] can increase rice biomass and yield, but the degree of this increase varies substantially among cultivars. Little is known about the gene loci involved in the acclimation and adaptation to elevated [CO₂] in rice. Here, we report on a T-DNA insertion mutant in japonica rice exhibiting a significantly enhanced response to elevated [CO₂] compared with the wild type (WT). The root biomass response of the mutant was higher than that of the WT, and this manifested in the number of adventitious roots, the average diameter of roots, and total root length. Furthermore, coarse roots (>0.6 mm) and thin lateral roots (<0.2 mm) were more responsive to elevated [CO₂] in the mutant. When exposed to lower light intensity, however, the response of the mutant to elevated [CO₂] was not superior to that of the WT, indicating that the high response of the mutant under elevated [CO₂] was dependent on light intensity. The T-DNA insertion site was located in the promoter region of the OsGF14b gene, and insertion resulted in a significant decrease in OsGF14b expression. Our results indicate that knockout of OsGF14b may improve the response to elevated [CO₂] in rice by enhancing carbon allocation to coarse roots and to fine lateral roots.

G protein γ subunit qPE9-1 is involved in rice adaptation under elevated CO2 concentration by regulating leaf photosynthesis

G protein γ subunit qPE9-1 plays multiple roles in rice growth and development. However, the role of qPE9-1 in rice exposed to elevated carbon dioxide concentration (eCO₂) is unknown. Here, we investigated its role in the regulation of rice growth under eCO₂ conditions using qPE9-1 overexpression (OE) lines, RNAi lines and corresponding WT rice. Compared to atmospheric carbon dioxide concentration (aCO₂), relative expression of qPE9-1 in rice leaf was approximately tenfold higher under eCO₂. Under eCO₂, the growth of WT and qPE9-1-overexpressing rice was significantly higher than under aCO₂. Moreover, there was no significant effect of eCO₂ on the growth of qPE9-1 RNAi lines. Furthermore, WT and qPE9-1-overexpressing rice showed higher net photosynthetic rate and carbohydrate content under eCO₂ than under aCO₂. Moreover, the relative expression of some photosynthesis related genes in WT, but not in RNAi3 line, showed significant difference under eCO₂ in RNA-seq analysis. Compared to WT and RNAi lines, the rbcL gene expression and Rubisco content of rice leaves in qPE9-1-overexpressors were higher under eCO₂. Overall, these results suggest that qPE9-1 is involved in rice adaptation under elevated CO₂ concentration by regulating leaf photosynthesis via moderating rice photosynthetic light reaction and Rubisco content.